1. Field of the Invention
This invention relates generally to a method and apparatus for recording and reproducing visual images or video signals, and more praticularly is directed to a method and apparatus for recording and reproducing such signals on a record medium which is in the form of a circular disc.
2. Description of the Prior Art
In the prior art, the most popular method of recording a video signal, such as a television signal or the like, is to record the same magnetically on a magnetic tape.
However, it is rather troublesome to reproduce the signal from a portion of the magnetic tape that is mid-way between its ends, and handling of the tape also creates problems. Further, the efficiency with which tapes can be reproduced from a master tape is low, and recording and reproducing apparatus for the magnetic tape is complex and expensive.
In order to avoid the above disadvantages, various methods have been proposed which use a recording disc as the recording medium on which the video signal is recorded in a spiral track. In one of these prior art methods, a recording disc with a highly reflective metallic layer is used, and a video signal, by way of example, is recorded in a spiral recording track. Along the length of this spiral recording track, there is formed a row or series of oblong depressions or pits. The oblong depressions are each the same in depth and width but vary in length and distance between adjacent depressions in response to the level of the video signal. In this case, the signal corresponding to, by way of example, one frame of the television signal is recorded in each circle or turn of the spiral recording track.
When the signal recorded on the above described recording disc is reproduced, the recording disc is rotated at high speed (1500 R.P.M.), the recording track is scanned by a light beam, such as a laser light beam, in the circumferential direction of the recording track, and the reflected laser beam is detected.
However, with the above recording method, the efficiency of utilization of the record disc for information recorded thereon is not very high, and consequently it is difficult to record on a single disc information, such as a wide band video signal, corresponding to a long time period. Further, since the recording disc must be rotated at high speed, uneven rotation of the recording disc is apt to produce jitter. Accordingly, the described prior art method requires the provision of a highly effective servo system for controlling the rotational speed and phase of the disc, and such a servo system is complex and expensive. In addition, controlling the tracking of the light beam on the recorded track is difficult and the mechanism required therefor is complicated.